The latest Welcome version (at this time of writing) is 17.10 (it’s the same for all releases, but it can only be provided by the Welcome PPA). The version in the Ubuntu archives is usually behind or cannot be updated because of SRU reasons.
Try adding the Updates PPA (which is the same as clicking “Get the latest listings” within Boutique) and try again:
sudo add-apt-repository ppa:ubuntu-mate-dev/welcome
sudo apt update
sudo apt install ubuntu-mate-welcome
This should give you the latest version which has corrected the fault.